'Their bodies were submerged, with only their heads coming in and out of the water.' Photograph: Alistair Levy for the Guardian

It was the summer of 1998 and I was living with my parents at our seafront house in Tenerife. I was trying to study for my engineering degree retakes in September – hard when it's sunny outside and your friends are at the beach.

I went up to the roof for a break and watched the 50 or so people sunbathing and swimming in the natural rockpool below our house. It was a typical Tenerife day – a blue, cloudless sky over a calm sea. But as I gazed into the distance, I spotted a series of three or four massive waves racing from the horizon towards the shore. I'd seen these mini-tsunamis many times before; they're known as mar de fondo or "sudden swell" and happen a few times a year in our part of the Atlantic. They must have been at least four metres high and were heading at speed in the direction of the pool. Most people know to look out for them, but from the screams that started coming from the beach, I could tell someone was in trouble.

Without thinking, I ran down into the street, grabbing my bodyboard on the way and yelling at a stranger to go inside my house and use the landline to call the coastguard. My neighbour Moises had heard the screaming as well and was also outside with his bodyboard, so together we rushed to the steps that led down to the sea.

Once we got closer, we spotted two people floating about 400 metres out. The waves had pulled them from the pool and into the open sea. Everyone was in a state of confusion. I knew that the nearest boat would take at least 30 minutes to reach us – we're not in a touristy area, and a long way from a marina. Waiting for help wasn't an option. I wasn't accustomed to this sort of emergency – I'd never been trained as a lifeguard – but I didn't think twice about trying to save them. I suppose in a way I wanted to impress everyone; at 19, a situation like that can seem like a good opportunity to show off.

Moises and I dived into the water and began paddling on our bodyboards towards the couple. The waves had receded but the sea was still rough and it took us 10 minutes to get to them. When we finally reached them, they were almost lifeless, bobbing around in the water like puppets, pale and motionless. They were young, not much older than 16. Their bodies were submerged, with only their heads coming in and out of the water. We could tell they were still alive from their small, gasping breaths but it was clear they wouldn't have been able to stay afloat much longer.

I grabbed the boy's torso and pulled him over my board, feeling no co-operation whatsoever; he was like a sack of floating potatoes. Moises hauled the girl on to his board. Their bodies were covered in scratches from where the waves had dragged them across the rocks. We discussed pushing them back to the shore, but we were too far out. We had to wait, trying to keep them perched on the boards, patting their faces to wake them up, telling them to be strong, all the while treading water to keep ourselves afloat.

As 30 minutes crept by I began to feel a bit scared. Keeping the couple on the boards was incredibly tiring. Finally, in the distance, we spotted a small Zodiac boat with three lifeguards heading towards us.

When the boat pulled up, we helped push the couple on board, only to be told that there was no room for us. It seemed pretty unprofessional to leave us there – we were a couple of miles from the shore. Exhausted, we used the last of our adrenaline to swim back in. People who had watched what happened came to meet us and check if we were OK, but there was no round of applause. Everything was back to normal.

That night, I stopped to think about the whole event. It all felt a bit weird. A friend had gone to the hospital and found out that the couple were in a stable condition, but that they probably would have died if they'd been in the sea for any longer. I knew it was a big deal that we'd saved them, but at the same time it didn't seem like that much effort. I was hoping to experience some sort of sense of wellbeing or peace for my good deed, but none of that came. I didn't feel like a hero. I'm sure that anyone who could swim would have done the same thing.